This invention generally relates to an apparatus for adjusting and locking the angular position of one member with respect to another which is especially applicable to the adjustment in inclination of the backrest of a seat, for example, an aircraft or railway seat, and the locking thereof by means of a piston cylinder unit. The piston cylinder unit is actuated by an operating cable controlled by push button mounted in the armrest of the seat.
Existing adjustable backrests for seats used in aircraft usually incorporate an hydraulic piston cylinder unit in conjunction with mechanical springs for adjusting the inclination of the backrest and the locking thereof in a desired position. The springs are provided to restore the backrest to its starting position when it is unloaded. The push button is mounted on the armrest and, when activated, releases the piston cylinder unit and the piston rod therein is displaced by the force of the springs acting on the unit. When the push button is released, the piston cylinder unit locks any further movement of the backrest. In this manner a seat back can be adjusted and locked as desired within a predetermined angular range.
The hydraulic piston cylinder unit together with the spring system is complicated and time consuming to install. However, these hydraulic piston cylinder units have been used almost exclusively in aircraft seating. One of the important advantages of these prior units was that little force was necessary to operate the push button and this allowed children and the physically impaired to actuate the device.
It is recently been found that in fires, the hydraulic piston cylinder unit tends to leak hydraulic fluid which is inflammable and which can add to the severity of the fire.
What has been needed and heretofore unavailable is a relatively simple piston cylinder unit which is easy to install and which will not leak hydraulic fluid at elevated temperatures. The present invention satisfies this need.